Modern subsea wellhead assemblies and Xmas trees are becoming more and more advanced. The sea depths at which they are applied are increasing, involving correspondingly larger pressures. In addition, modern drilling technology results in wells that extend deeper into the ground, resulting in high temperatures of the hydrocarbons flowing out of them. The temperature of the hydrocarbons can for instance be in the area of 150-200° C. and even higher in some cases. The wellhead assemblies are also exhibiting more features than before, and comprise equipment such as electric and hydraulic connections and conductors. As an example, such connections and conductors currently used elastomeric material sealing that tolerate temperatures in the range of −18° C. to 150° C., while there is a need for equipment that tolerate temperatures up to for instance 180° C. and above. Equipment for such conditions is difficult to make, and the needed materials are significantly more expensive.
Another type of component exposed to excessive heat is seals constituting pressure barriers. Being exposed to the high pressure differences in combination with possible large variations in temperatures requires excellent material characteristics and appropriate design.
In order to account for the higher demands on the wellhead components with regards to mechanical stability, combined with the elevated temperatures of the hydrocarbons flowing through it, one has thus sought out materials with extreme characteristics. This has met the demands on the components to great extent. However, with the conditions and demands on the equipment continuously increasing, the use of better materials is not sufficient.
Another way to take into account challenges resulting from the high temperatures is to provide a more clever design of the subsea wellhead assembly, such as the design of the Xmas tree. However, there is limited available space outside the hydrocarbon-containing flow in the bore of the Xmas tree, making it difficult to overcome said challenges in this manner.
U.S. Pat. No. 6,267,172 describes a method for exchanging heat between a pipeline through which fluid is flowable and an earth heat exchanger trough which heat transfer fluid flows.
U.S. Pat. No. 4,126,406 describes downhole cooling of the electric pump motor, motor protector, and thrust bearing of a submergible pump assembly in a high temperature environment.
U.S. Pat. No. 6,032,732 describes a system for heating the well head assembly of a conventional oil well pumper.
The present invention seeks to provide equipment for a subsea wellhead assembly, such as a subsea Xmas tree, capable of complying with such extreme requirements as mentioned above. In addition, the invention seeks to reduce the demands on the components of the equipment with regards to mechanical stability combined with high temperatures, thereby omitting the use of expensive components.